T lymphocytes play a critical role in host immunity to viruses. Unlike antibodies, which recognize free antigen, T cells recognize antigens in conjunction with class I and class II molecules of the major histocompatibility complex (MHC). In previous work, we characterize the class I restricted T cell response to influenza virus at the level of individual viral gene products and class I restriction elements. In the past year, we have used this information to investigate the role of class I molecule biosynthesis and transport in cellular processing of viral antigens or T cell recognition. To summarize our findings: 1. Active ribosomal synthesis of class I molecules is not required for processing of viral antigens for T cell recognition. 2. By contrast, antigen processing is completely inhibited by incubating antigen processing cells with Brefeldin A, a fungal metabolite known to inhibit transport of secretory and membrane bound proteins at a pre-Golgi complex location. 3. Consistent with this observation, antigen processing is deficient in a mutant cell line that exhibits a defect in membrane glycoprotein transport.